There is a strong demand to reduce the size of electronic systems. The size reduction is especially desirable in mobile electronics where space is a premium, but is also desirable in servers that are placed in big data centers since it is important to squeeze in as many servers as possible in fixed-size real estate.
One of the largest components in electronic systems includes voltage regulators (also referred to as power regulators). Power regulators often include a large number of bulky off-chip components to deliver voltages to integrated chips, including processors, memory devices (e.g., a dynamic random-access memory (DRAM)), radio-frequency (RF) chips, WiFi combo chips, and power amplifiers. Therefore, it is desirable to reduce the size of the voltage regulators in electronic systems.
Power regulators include semiconductor chips, such as a DC-DC regulator chip, that deliver power from a power source (e.g., a battery) to an output load. The output load can include a variety of integrated chips (e.g., an application processor, a DRAM, a NAND flash memory) in an electronic device. To efficiently deliver power, a voltage regulator can use a “buck” topology. Such a regulator is referred to as a buck regulator (also referred to as a buck converter). A buck regulator transfers charge from the power source to the output load using an inductor. A buck regulator can use power switches to connect/disconnect the inductor to one of multiple voltages, thereby providing an output voltage that is a weighted average of the multiple voltages. A buck regulator can adjust the output voltage by controlling the amount of time the inductor is coupled to one of the multiple voltages.
Unfortunately, a buck regulator is not suitable for highly integrated electronic systems. The conversion efficiency of a buck regulator depends on the size of the inductor, in particular when the power conversion ratio is high and when the amount of current consumed by the output load is high. Because an inductor can occupy a large area and is bulky to integrate on-die or on-package, existing buck regulators often use a large number of off-chip inductor components. This strategy often requires a large area on the printed circuit board, which in turn increases the size of the electronic device. The challenge is exacerbated as mobile system-on-chips (SoCs) become more complex and need increasingly larger number of voltage domains to be delivered by the voltage regulator.
Furthermore, a buck regulator is not well suited for high-speed charging of a battery. High-speed charging generally requires the use of a high input voltage. The use of a high input voltage, in turn, requires the buck regulator to provide a high voltage conversion ratio (VIN/VOUT) to convert a high input voltage (VIN) to an output voltage (VOUT) that is suitable for batteries. Unfortunately, at a high voltage conversion ratio, the efficiency of the buck regulator is substantially low, and the buck regulator wastes a large amount of power through heat dissipation. The heat dissipated by the buck regulator may raise the operating temperature of devices within the electronic system, which could cause malfunctioning. Therefore, the buck regulator is not well suited for high-speed charging of a battery.
Instead of a buck regulator, a high-speed charging system may use a switched-capacitor regulator to charge the battery. A switched capacitor regulator is known to be efficient even at a high voltage conversion ratio as long as the voltage conversion ratio is a ratio of integer numbers.